Suggestions on low undergrad GPA?

[shuaizh117]

Hi guys, just wanted to get some suggestions on my undergrad GPA.

I am an international applicant preparing my PhD applicant in Biomedical Research for 2022 fall semester. My undegrad GPA (major: biochemistry) was 3.1 from a TOP50 public university in the US, honestly I was not thinking of going to a grad school at that time so I didn't really focus on my study in college. After worked a few years in my own country (a non-biomecial field), I came back to the US and got my master's in biology, and my GPA was 3.8. I was thinking of going to a PhD program but I knew my background is still not competitive, so upon graduation, I started to work in a research institute at a TOP3 hospital in the US and it has been 4 years. I work independently and  have several publications (1st and co-) and multiple oral and poster presentations in the last few years. 

Do you think I should briefly explain my low undegrad GPA in my PS? Honestly, I applied to several top programs in the US last year but got rejected from all. I understand it's very competitive for international applicants, but I was wondering if my low undergrad GPA negatively affected my application? Please suggest. Thank you!